trouble with whirlpool pump before flame out

I've recently gone through a bunch of upgrades to my system, and last weekend was the first time for me to use an immersion chiller and a pump to whirlpool. A few minutes before flame out I opened up the valve on my boil kettle and started trying to recirculate, but I had a ton of trouble trying to get it to keep prime. After I started cooling, it got a lot better.

It seems like the pump was pulling pressure and causing the near boiling water to boil, making it hard to keep the pump primed. As the wort cooled, the cavitation became less of an issue?

Is that really happening, or am I overthinking this? Does anyone else have trouble with their whirlpool pump while the wort is still boiling?

This can happen. When you lower the pressure the boiling point is lowered also. You can lessen this by making sure there is no restriction to the input side of the pump. If you need to restrict make sure it's on the output side. Also, you can reduce cavitation of the pump by making sure the output side is higher than the input side. Any bubbles will naturally surface and easily make their way out the higher output side.

Tell how your pump, valves, and hoses are oriented.

I use a March pump to whirlpool and found I had the same problem originally. I've since learned (from here) to restrict the incoming flow about 50% with the ball valve on the kettle. From what I've seen the boiling wort causes the damn bubbles in the pump and by slowing down the flow the pump can get the bubbles moving. Once the wort has cooled some I can turn on the flow full blast. I always restrict on the input side when ever I use my pump because I use silicone tubing. Never had it happen but there are warnings that the tubing can only take 10psi or they will burst. Not gonna risk that....

http://www.bargainfittings.com/index.php?route=product/product&path=52&product_id=122

Hammy71 said:

I use a March pump to whirlpool and found I had the same problem originally. I've since learned (from here) to restrict the incoming flow about 50% with the ball valve on the kettle. From what I've seen the boiling wort causes the damn bubbles in the pump and by slowing down the flow the pump can get the bubbles moving. Once the wort has cooled some I can turn on the flow full blast. I always restrict on the input side when ever I use my pump because I use silicone tubing. Never had it happen but there are warnings that the tubing can only take 10psi or they will burst. Not gonna risk that....

http://www.bargainfittings.com/index.php?route=product/product&path=52&product_id=122

Click to expand...

Wow - never saw that warning and that's the tubing I use. No worries though since the output ball valve is directly on the pump housing. That's where I restrict the flow. Interesting too that the warning is to restrict on the input side of the pump. I'm pretty sure that Walter from March Pumps insists on restricting on the output side.

stlbeer said:

Wow - never saw that warning and that's the tubing I use. No worries though since the output ball valve is directly on the pump housing. That's where I restrict the flow. Interesting too that the warning is to restrict on the input side of the pump. I'm pretty sure that Walter from March Pumps insists on restricting on the output side.

Click to expand...

The warning is in regard to the tubing, not the pump.

stlbeer said:

Wow - never saw that warning and that's the tubing I use. No worries though since the output ball valve is directly on the pump housing. That's where I restrict the flow. Interesting too that the warning is to restrict on the input side of the pump. I'm pretty sure that Walter from March Pumps insists on restricting on the output side.

Click to expand...

The warning says:
"10 psi max pressure - DO NOT RESTRICT ON THE OUTPUT SIDE OR YOU WILL POP THE TUBING"
That is for the tubing not the pump. The tubing will have normal pressure in it from the kettle to the pump. The valve on the pump output can be shut off and it doesn't change the pressure in the input tubing.

Edit: Catt22 - I type very slowly.

Thanks guys. I know that was for the tubing. Sometimes my fingers don't type what I think. I'm still surprised the 10 PSI is all it takes to burst a 1/8" wall silicone hose.

At any rate, this is the post I was thinking of regarding pump cavitation and inlet restriction.

https://www.homebrewtalk.com/f11/questions-about-march-pumps-answered-factory-210199/index6.html

P-J said:

The warning says:
"10 psi max pressure - DO NOT RESTRICT ON THE OUTPUT SIDE OR YOU WILL POP THE TUBING"
That is for the tubing not the pump. The tubing will have normal pressure in it from the kettle to the pump. The valve on the pump output can be shut off and it doesn't change the pressure in the input tubing.

Edit: Catt22 - I type very slowly.

Click to expand...

FYI - 10psi is about 20 feet of head. Imagine a column of water 20 feet tall. that's what it would take to produce that pressure. If your system has the valve mounted on the outlet of the pump itself, then there is absolutely no risk here. Hammy, restricting the flow by the kettle valve is only going to cause more cavitation in the boiling wort. The solution here is to open the kettle valve all the way, and throttle the output on the pump. I also have this problem because my piping is all 1/2", but my pickup tube is 3/8". After you have gotten the wort below about 190F there ought not be any more cavitation, and you can open the valve more. I don't usually end up with it open all the way because it sucks the hops onto the screen, and it gets clogged. YMMV.